We put forward that the unique embryological origins of individual mammalian calvaria impact differences in their osteogenic capacity. The cental hypothesis of this proposal is that differences in embryonic origins of calvarial osteoblasts affect their embryonic and post-natal osteogenic potential and skeletal regenerative capacity. The paired parietal frontal bones in the anterior skull are derived from the neural crest and the paired parietal bones, positioned posteriorly, are derived from the paraxial mesoderm. We have preliminarily observed the frontal bone to possess superior osteogenic potential both in vitro and in vivo compared to the parietal bone. Our proposal aims to verify this difference in osteogenic potential and elucidate the role of fibroblast growth factor (FGF) signaling underlying this disparity. Such an understanding is of central importance to overcoming current challenges with treatment of calvarial defects. The inability of humans older than one year of age to reossify calvarial defects poses a substantial burden on our healthcare system. Current use of autogenous grafts, allogeneic substances, and synthetic materials to reconstruct calvarial defects are all suboptimal. These inadequacies serve as the impetus for our application. Through the identification of calvarial bones with inherently superior osteogenic capacity, we seek to gain insight into novel strategies for robust calvarial regeneration. In Specific Aim 1, we will determine the role of FGF signaling in mediating differences between neural crest-derived frontal and paraxial mesoderm-derived parietal bone osteoblasts. Will begin by comparing the expression profile of key FGF ligands and receptors, and the activation of their downstream mediators, between the frontal and parietal bones of the wild-type and transgenic mice described above. In Specific Aim 2, we will determine if the reduced healing capacity of paraxial mesoderm-derived parietal bone is augmented by the addition of exogenous FGF-2, -9, and -18 after injury in wild-type mice. In Specific Aim 3, we will determine if the robust healing capacity of neural crest-derived frontal bone is reduced or negated in transgenic mice possessing fgf-2-/-, -9-/-, and -18-/- loss of function mutations. Ultimately, the translational goal of this application is to identify key molecular mechanisms in the FGF family that promote robust bone regeneration. We assert that the identification of calvarial bones with superior osteogenic capacity will provide insight into such mechanisms.